Effect of dietary mineral sources and oil content on calcium utilization and kidney calcification in female Fischer rats fed low-protein diets.

We studied the effects of dietary mineral source and oil intake on kidney calcification in 4-wk-old female Fischer rats after consuming the AIN-76 purified diet (AIN-76). A modified AIN-76 mineral mixture was used, although the original calcium (Ca)/phosphorus (P) molar ratio remained unchanged. Rats were fed the modified diets for a period of 40 d before their kidneys were removed on the last day. Ca balance tests were performed on days 31 to 36 and biochemical analysis of urine was also studied. Kidney Ca, P, and magnesium (Mg) in the standard diet group (20% protein and 5% oil) were not affected by the mineral source. Kidney Ca, P, and Mg in the low-protein (10% protein) diet group, were found to be influenced by the dietary oil content and mineral source. In particular, the different mineral sources differentially increased kidney mineral accumulation. Pathological examination of the kidney showed that the degree of kidney calcification was proportional to the dietary oil content in the 10% dietary protein group, reflecting the calcium content of the kidney. The information gathered on mineral sources in this study will help future researchers studying the influence of dietary Ca/P molar ratios, and histological changes in the kidney.

Effect of the protein and oil contents on calcium utilization in the diets of female Fischer rats that were fed by three different feeding methods.

We studied the effects of varying the protein and oil contents in the diet and three different feeding methods on the utilization of dietary calcium (Ca) in female Fischer rats. The experimental diets were based on the AIN-76 diet. Rats were fed one of nine experimental diets containing different levels of protein and oil. The experimental diets contained 10, 20 or 40% of protein (milk casein) and 5, 10 or 20% of soybean oil. The three meal feeding methods were ad libitum feeding, pair feeding and adjustable feeding. The experimental diets that were given by prepared feeding were supplemented with a mineral and vitamin solution. The effects of the protein and oil contents in the diet were analyzed by two-way ANOVA. Among rats that were fed ad libitum, the oil content in the diet affected the degree of mineral and vitamin intake. Among the rats fed ad libitum, the oil content in the diet had a significant effect on the level of Ca intake, although it did not have a significant effect on the level of energy intake. For pair feeding, the feeding volume was limited in each group; therefore, there was a significant difference in energy intake and there was no significant difference in Ca intake among each diet group. For adjustable feeding, there was considerable mineral and vitamin intake, which effected the reduction of feeding volume depending on the oil volume in the diet. There were no significant differences in the energy, Ca and other mineral and vitamin intakes among the nine groups that were fed using adjustable feeding. In analyzing two-way ANOVA, in which the parameters were the contents of protein and oil in the experimental diets, there were differences in Ca utilization among rats that were fed using the three feeding methods. This result was shown to reflect on the difference as energy, mineral including Ca, and vitamin intake. However, the protein content in the diet had a significant effect on urinary Ca excretion in all three feeding methods. In addition, it was clear that the intake of protein and oil affected kidney calcification in all three feeding methods. The AIN Experimental Diet Committee reported that kidney calcification was found among rats that were fed the AIN-76 diet and that one of the causes of kidney calcification was the Ca/P ratio in this diet. The protein and oil contents in the diets had significant effects on the degree of kidney calcification among rats that were fed by pair feeding or adjustable feeding. The results of this study suggest that the protein and oil contents in the diet play an important role in kidney calcification.